1. Technical Field of the Invention
The present invention relates in general to the field of control systems, and in particular, by way of example but not limitation, to adaptive control for telecommunications systems that have measurements of varying time-delays.
2. Description of Related Art
Mobile wireless communication provides many benefits to subscribers of wireless communications services, such as safety, convenience, improved productivity, and simple conversational pleasure. One prominent mobile wireless communication option is cellular communication. Cellular phones, for instance, can be found in cars, briefcases, purses, and even pockets. Cellular phone use is proliferating both because it provides these benefits and because the expense of using cellular phones continues to decrease. One manner to continue decreasing the cost of cellular phone use is to improve the control of cellular systems (e.g., increase the efficiency of infrastructure utilization).
A typical cellular system is composed of a number of mobile stations (MSs), each of which is connected to one or more base stations (BSs) via a radio interface (e.g., which is normally based on a pre-established standard). Usually, one BS handles the traffic in a given area, such as a cell. The BSs are further connected to a radio network controller (RNC), which in turn communicates with a mobile switching centre (MSC). MSCs are also connected to a fixed network (e.g., a public switched telephone network (PSTN), an integrated services digital network (ISDN), the Internet, etc.) in some manner. Additionally, at least one home location register (HLR) is typically present and accessible from the MSCs. Each individual BS, RNC, MSC, and HLR object may in general be considered a network element (NE). The collection of NEs together form the xe2x80x9cnetworkxe2x80x9d.
An important task of the NEs is to collect measurements and compute various system quantities, such as the bit error rate (BER), the signal to interference ratio (S/I), the number of successful access attempts (NSAA), the NE traffic load (NETL), etc. These xe2x80x9clow-levelxe2x80x9d quantities are passed to a radio network operation (RNO) system for further analysis, depending on which system modifications may be commanded (e.g., ordered, instructed, etc.), either manually or automatically. The automatic mode of operation is becoming increasingly important because (i) the complexity of systems is rapidly increasing, thereby making it difficult to handle all operations fully manually, and (ii) an automatic solution has the ability to react to changes much faster than a manual one, which can result in an increase in the revenue of the operator of the system.
However, for an automatic control solution to be feasible, it is crucial in conventional systems that the measurements are delivered in xe2x80x9creal-timexe2x80x9d. It should be noted that the intended meaning of xe2x80x9creal-timexe2x80x9d may vary depending on the intended application of the measurements. For example, at times the measurements should be delivered on a millisecond basis, and at other times it may be sufficient to acquire measurements every day or so. For an RNO system that focuses on control of a region or network, the typical granularity desired is on the order of seconds or sometimes minutes.
Today""s RNO systems include very few, if any, automatic control functions. The ones that are realized focus on control on a NE level, where it may be assumed that new and fresh measurements are regularly available. The special problems encountered when performing automatic region and/or network level control in a cellular system have not been studied in significant detail, much less solved. In fact, the control community has heretofore failed to address with any substantial attention the problems within this domain.
Assume, by way of example, that an operator has defined a geographical area (e.g., governed by a number of NEs) in which a concept, such as the overall traffic load (OTL) in the area, has been defined. The computation of this overall traffic load is then based on measurements, such as the individual NETLs, delivered to the RNO system from a number of NEs. Assume also, by way of example, that the operator has specified a desired maximum allowed traffic load (MATL) (e.g., a reference signal). Based on the computed overall traffic load and the desired maximum allowed traffic load, a controller would order changes in/to the NEs so that the actual (and computed) traffic load remains beneath the desired maximum value, even though the requested traffic varies.
The problem with such an automatic control solution is that the computed traffic load is based on measurements of different ages (unless the entire system is synchronized, which is highly unlikely in conventional systems). Consequently, if the control system is fed with xe2x80x9ctoo oldxe2x80x9d measurements, the system becomes unstable, which should be avoided at any cost. A common conventional technique of handling this problem is to design the controller(s) for the worst possible age of the measurements (which, in practice, is something that is very hard to determine in any event). In terms of controller design, the consequence is that the closed-loop gain must be reduced, which leads to a slower system response. Unfortunately, this slower system response occurs even when all the measurements are xe2x80x9cfreshxe2x80x9d. Using this conventional approach, stability is achieved but at the expense of performance, regardless of the age of the measurements. In summary, conventional control systems have heretofore only achieved stability in systems with measurements of differing age by slowing system response in accordance with the estimated oldest age of all of the applicable measurements.
The deficiencies of the prior art are overcome by the method and system of the present invention. For example, as heretofore unrecognized, it would be beneficial if a telecommunications control application was designed to be adaptive in its response to measurements of varying age. In fact, it would be beneficial if an adaptive component slowed control system response when measurements on which the control system response were determined were xe2x80x9colderxe2x80x9d. Consequently, such an adaptive component ameliorates the trade-off between system performance and system stability under operational conditions that include measurements of varying time-delays.
The method and system of the present invention enables the changing of the gain in a closed loop (e.g., self-configuring) telecommunications system based on the age of the available measurements. A high gain is used when measured data are xe2x80x9cfreshxe2x80x9d, so as to obtain a good performance (e.g., a fast response) for the telecommunications system. The gain is then reduced as the age of the measurements increases. The decreased gain results in a slower system response, but this is a desirable result in order to preserve stability. The system and method may be applied, for example, in many mobile telecommunications systems (e.g., a Global System for Mobile Communications (GSM) system, a Wideband Code Division Multiple Access (WCDMA) system, etc.) that include a number of distributed network elements. In one embodiment, the system and method of the present invention modify the closed loop gain in an adaptive fashion and use one or more fuzzy membership functions for specifying what is meant by xe2x80x9cfreshxe2x80x9d measurements.
An important technical advantage of the present invention is that it enables a control system of a telecommunications system to operate with measurements of varying age.
Another important technical advantage of the present invention is that it provides an ability to de-emphasize xe2x80x9colderxe2x80x9d measurements in favor of xe2x80x9cnewerxe2x80x9d measurements.
Yet another important technical advantage of the present invention is the ability to improve control system response time in a telecommunications system by applying a high gain when measurements are xe2x80x9cfreshxe2x80x9d to achieve a fast response time and a lower gain when some or all measurements are xe2x80x9ctoo oldxe2x80x9d to ensure system stability.
Yet another important technical advantage of the present invention is that it may be utilized in a wireless communications system for implementing automatic control of network-level adjustments.
Yet still another important technical advantage of the present invention is that it may be advantageously applied to and/or implemented in conjunction with an Internet Protocol network (IP-net), etc.
The above-described and other features of the present invention are explained in detail hereinafter with reference to the illustrative examples shown in the accompanying drawings. Those skilled in the art will appreciate that the described embodiments are provided for purposes of illustration and understanding and that numerous equivalent embodiments are contemplated herein.